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Which of the following statements about nuclear processes are ALL CORRECT? (P) In alpha decay, mass number decreases by 4 and atomic number decreases by 2. (Q) In beta-plus decay, mass number remains unchanged while atomic number decreases by 1. (R) In nuclear fission, the parent nucleus breaks into two fragments of nearly equal mass. (S) In proton emission, both mass number and atomic number decrease by 1.

1. P, Q, R and S
2. P and Q only
3. P, Q and S only
4. P and S only

Correct answer: P, Q, R and S

Solution

P: Alpha particle is He-4 (A=4, Z=2); daughter has A reduced by 4 and Z reduced by 2. TRUE. Q: Beta-plus decay converts a proton into a neutron inside the nucleus, emitting a positron (A=0, Z=+1 for positron); total A unchanged, Z of nucleus decreases by 1. TRUE. R: Fission of a heavy nucleus (e.g., U-235) typically yields two large fragments of comparable mass (asymmetric but approximately equal). TRUE at NCERT textbook level. S: Proton emission: daughter has A-1 and Z-1. TRUE.

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